1. Field of Invention
With the advent of the world needing more and more energy and the need to explore deeper and deeper into the earth for oil, greater emphasis is placed upon the need for improved drilling techniques.
2. Description of Prior Art
Deep well holes are lined with steel casings. The casings are awkward to handle because of their great length and weight. The sections of casing are provided at each end with a thread, usually a conical fine-pitch thread. To line the bore hole with casing, the last section added to the string is lowered into the bore hole until only the upper threaded portion projects above the top of the bore. In order to be able to join two successive casings by means of the screw threads, the next casing is raised, as by means of a crane or the like, until the lower threaded end of the pipe section is above the upper threaded end of the last downhole section of casing, which has previously been suspended on the rig floor, and secured against rotation, by means of wedges. The raised section of casing is then lowered with its threaded lower end into the threaded sleeve at the upper end of the downhole casing. Next the raised section of casing has to be brought into accurate axial alignment with the downhole section of casing. This alignment is achieved manually usually from a temporary work platform suspended near the top end of the raised section of casing. Once alignment has been achieved, the raised section of casing is rotated to form a threaded connection with the downhole section of casing. Accurate axial alignment has to be maintained while rotating the upper section of casing, or damage to the threads will result. To align, and even more to maintain alignment while rotating, requires considerable strength and visual judgment by personnel on the operation. The method can be time consuming. Difficulties in aligning the sections, and maintaining such alignment, are considerably aggrevated in an off-shore environment, where frequently high winds and wave induced movements of the drilling rig strongly counteract efforts to align the casing sections. Thus, the reliability of a casing joint and the speed of the operation depends upon the muscular strength and the skill of estimating by sight of the operators.